The results of investigation of the photodissociation dynamics of triatomic Bose-condensed ultracold molecules (trimers) with the formation of atoms and diatomic (dimer) pairs are presented. The interaction Hamiltonian is proposed, and a system of nonlinear equations is constructed that describes the evolution of atoms and molecules. Integrals of motion are obtained, and a nonlinear differential equation is derived for the time evolution of the atomic density with the use of these integrals. The solutions of this equation in various approximations imply that, depending on the initial conditions, different regimes of time evolution of the system are possible: periodic and aperiodic regimes.